How to Handle Brown Spots on Basil Leaves

If you have been growing basil in your garden for quite some time, you would notice that some plants would have leaves that have brown spots. You might be thinking that these leaves are automatically bad and that you shouldn’t eat them. After all, the main reason why people raise basil plants in the first place is to clip the leaves to add to their favorite Italian dish.

Whether we’re talking about a few whole basil leaves arranged on a margherita pizza, or ground up in a pesto pasta sauce, basil is quite a standby in traditional classic Italian cuisine. Seeing brown spots on basil leaves might seem like a monkey wrench has been thrown into your Italian gardening plants. But in the big scheme of things, it’s not that big of a deal.

What Causes Brown Spots on Basil

What Causes Brown Spots on Basil?

There are several reasons why basil would develop brown spots. Almost all of these have to do with other microorganisms. In other words, the plants are infected. The most common is fusarium wilt.

Fusarium Oxysporum

There’s a fungus in the soil that is called fusarium oxysporum. This fungus is spread through transporting infected soil from one plant to another.

Fusarium wilt usually creates brown spots on basil leaves until the plant eventually dies. The reason for this is that fusarium oxysporum kills the plant’s ability to transport water. Without water transport from the roots, the basil plant eventually dies. So, if you see brown spots and a lot of your leaves are beginning to wilt, you might have a case of fusarium wilt on your hands.

Fungal Leaf Spot

Fungal leaf spots are caused by another fungus called colletotrichum. This fungus attacks only the leaves.

At first there would be a small spot, and then the leaf would start to brown, and eventually, it will fall off. This tends to be fairly localized to the leaves. Now, depending on how severe the infestation of this leaf-based fungus is, your basil plant might end up dying.

In fairly controlled infections, just a few leaves are affected. They look really bad, and they start to fall off. But since they don’t really have much contact with the rest of the plant, all the other leaves are spared.

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In extreme cases, all leaves are pretty much infected, and this leads to your basil plant completely shedding its leaves. Just as getting its water transport system cut off by fusarium wilt is fatal, completely losing its leaves due to fungal infection is equally bad.

While you can’t do much about fusarium wilt, you can do a lot to prevent fungal leaf spots. Be proactive. Once you see infected leaves, just cut them off quickly. As much as possible, cut off whole branches. This usually does the trick unless there’s a spot that you missed.

Downy Mildew

First, the good news. Downy mildew is not usually fatal to basil plants, but they can be annoying. Basically, when you see yellowing or browning on the leaves, this is just the beginning of downy mildew infestation.

You have to look under the leaves to see if there is some sort of fuzzy powder present there. This is a clear indication of downy mildew.

To avoid this problem, make sure you get clean seeds. Also, try to water the roots of your basil plants as directly as possible. Downy mildew requires moisture to thrive.

Cercospora Leaf Spot

It’s a common mild fungal infection caused by too much moisture on the plant.  The common culprit is an overhead irrigation system that keeps the basil soaked in water beads. It may also be from improper watering of the plant by hand. 

Simply put, you don’t want your basil always draped in moisture. It’s the ideal condition for different types of fungal infections to develop, and not just Cercospora. The trick is to keep your basil dry by carefully watering the soil around it.

Some growers love to mist their plants regularly, which is one of the worst things that you can do. Sure, you can rinse your basil with water every once in a while if it becomes dusty or dirty. Ironically, it can even wash out fungal spores. However, you have to make sure the plants don’t get wet for extended periods, as it will allow the fungus to germinate.

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Cercospora is pretty easy to get rid of if you spot it early. Just prune the infected leaves and dispose of them properly.

Can You Eat Brown Basil Leaves

Preventive Measures

Generally speaking, never get water on the leaves.  As much as possible, water the soil near and around the base of your basil.  Spacing your plants a bit further apart would help stop the spread of diseases. You could also try to put a layer of mulch around the basil to keep it healthy.  

Is it Safe to Use Fungicides?

Organic fungicides are the most trusted by gardeners who grow their own vegetables to eat.  Here are a few we recommend:

  • GardenSafe Fungicide3 – This one does several jobs. It serves as an insecticide, fungicide, and miticide. It’s a triple threat! It is also OMRI (Organic Materials Review Institute) listed, so you can rest assured that you’re using an organic product on your basil babies!
  • Trifecta Crop Control – Another triple threat product! And it is also OMRI listed! It is on the pricier side, but it comes highly recommended by gardening pros.

Furthermore, fungicides can either be curative or preventive.  The preventive ones are applied to keep the fungus from developing on plants.  Curative ones are more of a last resort and used when an infection has already set in. Some fungicides can do both.

Can You Eat Brown Basil Leaves?

Here’s a rule of thumb. As long as there are no fungal powders from downy mildew or fungal slime on the otherwise brown-spotted leaf, you can actually eat it. The question is whether you want to eat it because the flavor profile might not be there.

But assuming that you’re looking to use as much of your basil plant as possible, you can safely eat browned basil leaves.

There are alternative uses. You can dry these leaves and add them to your Italian spice mix. You can use brown leaves in the bottom of sandwiches to add a little bit of basil flavor. You can cut out the nasty-looking parts and add the bits and pieces to fresh salads.